The delivery of high intensity radiation to cancerous body tissue with a highly focused delivery is complicated by subject movement during the radiation administration session. While bolting a subject skull into a frame has proven to be partially successful, cervical flexion and respiration still contributes to radiation delivery defocus. While anesthesia has proven partly successful in compensating for cervical flexion and respiration, the difficulties and possible complications associated with anesthesia make this an unattractive option.
Treatment of a lesion located in the thoracic or abdominal cavity exacerbates the problem associated with patient movement. With a diaphragm traveling about 10 cm in an adult human, dynamic positional change of organs is observed during a respiration cycle. The result of organ movement is a radiation delivery defocus with tissue surrounding a lesion being subjected to unintended dosing.
Prior art attempts to address physiological movement during radiation dosing have met with limited success. Typical of these systems is the establishment of a camera array around the three-dimensional subject volume. A series of blinking lights secured to subject skin are tracked by the cameras and through geometric triangulation, the location of a surgical tool, catheter tip, or fiducial marker is noted. However, owing to the slow speed associated with such a system, the scans are typically performed prior to a surgical procedure or during an interruption in the procedure and, as such, lack real-time responsiveness needed for radio-dosing. A variation on such a system uses reflective spheres secured to the subject with pulsing lights proximal to the cameras in order to approximate volume through triangulation. These methodologies have met with limited acceptance owing to the inability of the optical system to simultaneously detect a fiducial marker or medical instrument internal to the subject volume while computing volume changes associated with respiratory physiology.
A more sophisticated prior art approach to this problem achieves a five second lag time relative to subject motion and is available under the trade name CyberKnife®. This method uses a series of magnetic resonance imaging or computed-aided tomography images to compute hundreds of planar x-ray images prior to a procedure. The procedure occurs on a fluoroscopy table with fluoroscopy images being compared by a computer to the computed x-ray images to ascertain biplanar fluoroscopy image pattern match with the computed x-ray images so as to determine subject position. This process has met with limited acceptance owing to a five second lag being a considerable time period as compared to a respiratory cycle. Additionally, a subject must be semi-restrained in order to derive a therapeutic effect.
To further improve the compensation for respiratory physiology, a constellation of radio-opaque fiducials are implanted within the subject volume that is to be the subject of the therapy and the procedure repeated of collecting MRI or CT scans from which biplanar x-ray images are derived prior to a therapeutic session. The computed biplanar x-rays are compared with fluoroscope images collected prior to or during a procedure, which still further reduces the lag time during the computed respiratory cycle position and the actual body position. While a constellation of fiducials made up of skin marks or markers placed on the chest wall afford a timing of respiratory physiology-related movement, a time lag still persists.
Thus, there exists a need for a fiducial marking system capable of calculating a target movement within a subject related to subject movement on a greater precision than has been heretofore available. Additionally, there exists a need for a fiduciary marking system capable of predicting periodic subject movement so as to further define radiation dosing.